Each winter, we get a lot of service calls for smoking heat pumps, usually on or right after the first very cold night of the season. In almost every case, the outdoor unit makes a loud, terrible noise and has smoke coming out of it. While this situation may be alarming, it’s actually quite normal, especially on the first cold late fall or winter night.
What’s the Smoke?
We’ve explained how heat pumps work in another blog post, but the long and short of it is that heat pumps absorb heat from outdoors and bring it indoors in heating mode. In cooling mode, they do the opposite (like a traditional air conditioner). To switch between modes, there is a part called a reversing valve that redirects the flow of the heat-absorbing fluid inside (refrigerant, or it may be called by the brand name “Freon”).
The reversing valve also switches when frost builds up on the unit and a defrost cycle starts. (Temperature sensors and possibly timers indicate when defrost should start.) Running the unit in cooling mode without the fan helps melt frost off the outdoor coil because the refrigerant is hot. Some of it might melt rapidly enough to evaporate, and then when it hits the cold air, it creates steam.
While it may look like smoke from a distance, this white or clear steam is just like what you’ll see over a cup of hot coffee or tea. It happens whenever moisture evaporates and then cools enough to form water droplets. It’s natural and harmless, so there’s no need to call an HVAC contractor.
What’s the Loud Noise?
A loud whooshing noise (and even one with a bit of vibration and grinding) that lasts about 15 seconds or less is usually normal. This loud noise also has to do with the reversing valve. When this valve moves, the refrigerant changes directions, so the pressures get thrown off inside the system. It takes a few seconds for those to even out again. The system should go back to normal right after.
The fan also stops when a system goes into defrost. The fan makes quite a bit of noise, so shutting it off will make the other noises in the system seem louder.
What NOT to Do During Defrost
The noises and steam from the defrost cycle may be alarming, especially if you aren’t very familiar with heat pumps. However, since the defrost cycle is a normal process in a heat pump, you want to avoid turning off your heat pump when you notice it happening. Turning it off will just delay the defrost, which leaves the frost on the unit.
You’ll also almost NEVER set the unit to emergency mode in Florida. The emergency mode shuts down the heat pump and runs only the emergency heat. Backup heat in emergency mode is expensive, and we almost never see temperatures that would require it in Central Florida, so we want to avoid using it.
But I Hear Something Else!
Other sounds, especially those that last longer than the 15 seconds or so it takes for the refrigerant pressures to even out, may indicate a problem with your heat pump. Keep an ear out for the following noises:
- Electrical buzzing
- Banging
- Chattering
- Squealing
These noises are not normal, and a qualified HVAC technician should diagnose the issue and provide a solution. There may be a problem with one of the electrical parts, the fan motor, or the compressor.
If your heat pump is making any of the noises that aren’t normal for a typical defrost cycle, your best bet is to call an HVAC contractor to help get to the root cause.
Our phones are open 24/7 at Kalos, so you can call or text (352)-243-7099 at any time, and we’ll be more than happy to gather some information about your issue and schedule a technician visit.
